Gaining access to the heart is a continued challenge in cardiovascular medicine. Conventional procedures for accomplishing tasks such as valve replacement generally involve a thoracotomy and/or creation of one or more access ports across the wall of the heart itself, which is relatively highly invasive and therefore undesirable. Recent progress has been made in the area of percutaneous intervention, wherein instrumentation, such as catheters, guidewires, and prostheses, are brought to the heart through the vessels connected to the heart. One of the challenges with percutaneous approaches to procedures such as valve replacement, is that patients with diseased valves often have diseased major vessels, and the instrumentation required to accomplish a procedure such as a percutaneous valve replacement is often fairly large. For example, the un-expanded delivery size of a CoreValve® aortic valve prosthesis available from Medtronic, Inc. is approximately 18 French; the un-expanded delivery size of a Sapien® valve available from Edwards Lifesciences, Inc. is between 18 and 24 French, depending upon which size is utilized. Such outer sizes do not allow for a conventional guide catheter to be inserted as a protective layer between the tools and the tissue, and therefore the standard of care has become direct insertion of the valve instrumentation through the diseased vessels to reach the target location within or adjacent to the heart. Another complicating factor with such interventions is the fact that it is likely that the aorta through which the devices will be advanced will be diseased (one recent study concluded that 61% of patients over 65 years of age with severe aortic valve stenosis also have severe aortic atherosclerosis; Osranek et al., American Journal of Cardiology, 2009; 103: 713-717). FIG. 1 illustrates a typical diseased aorta (2) with deposits (4) clinging to almost all interior surfaces. This complicated surgical paradigm has led some clinical researchers to believe that elevated stroke rates associated with such procedures may be related to the physical insertion of large interventional tools through diseased vessels and concomitant scraping or microscraping action of the tools against the diseased vessel walls, which is breaking portions of plaque loose and allowing these to flow with the bloodstream into the brain and other undesirable landing places. There is a need for a configuration wherein a relatively thin but protective sheath-like member can be put in place to guide the interventional tools and prosthesis while mitigating load concentrations and/or scraping or abrasion of the interior of the subject vessels. The subject invention is directed to address such need.